This application claims priority to German Application No. DE 198 59 328.7, filed Dec. 22, 1998, the disclosure of which is incorporated herein by reference.
The present invention relates to an axial piston pump of a swash plate variety having a driven rotating cylinder block or drum and a large number of cylinder bores arranged radially therein, each of the bores being separated within the cylinder drum by a web of cylinder drum material. Pistons are arranged in each of the cylinder bores to be reciprocatingly movable in an axial, linear direction relative to the rotation of the cylinder drum between, at the end of a de-compression stroke, a bottom dead center position and, at the end of a compression stroke, a top dead center position. A valve plate having a low pressure connection port and a high pressure connection port also is provided, with the low and high pressure connection ports being separated in the valve plate by a web of valve plate material. The rotation of the cylinder drum causes the cylinder bores to be aligned in alternating fashion with the low-pressure connection port and the high-pressure connection port. Concurrently, the cylinder bores sweep past the web in the valve plate separating the low and high pressure connection ports, whereupon a reversing capacitance in fluid communication with the sweeping cylinder bore via at least one channel is supplied through the valve plate to mitigate the effects of a pressure pulsation.
The structure and operation of axial piston pumps of the type herein involved is described in further detail in the publication xe2x80x9cMeasures For The Reduction Of High-Pressure-Side Pulsations Of Hydrostatic Swash Plate Unitsxe2x80x9d by Marcus Jarchow, Dissertation 1997, Aachen Institute of Technology, Verlag Mainz, Aachen, and in the following U.S. Pat. Nos.: 3,250,227; 3,667,867; 3,774,505; 4,037,521; 4,212,596; 4,366,627; and 5,123,815. The Jarchow publication deals in particular with the problem of high-pressure-side pulsations, and sets forth a solution which involves a reversing capacitance. In this regard, in order to avoid compression oil flows when each individual cylinder bore of the cylinder block is aligned with the high-pressure connection port, it is necessary to adjust the pressure forming in the cylinder bore through the compression movement of the piston to the pressure prevailing on the high-pressure side of the control base in its high-pressure connection port. Through the use of a reversing capacitance, this adjustment is effected by admitting compression oil under high pressure into the cylinder bore. This reversing capacitance is formed in the control base via a channel in communication with the cylinder bores of the rotating cylinder block and, respectively, via an additional channel with the high-pressure connection port.
It has been observed, however, that the undesirable high-pressure-side pulsations continue to occur in attenuated form even with the use of a reversing capacitance. In this regard, the clearing of the channel extending from the reversing capacitance through the web between each of the cylinder bores results in an abrupt pressurization of the cylinder bore as the compression oil is admitted under high pressure from the reversing capacitance. An object of the present invention therefore is to further reduce the development of pulsations in an axial piston pump, and to ensure a less abrupt alignment of the cylinder bore with the high-pressure connection port.
Broadly, the present invention is directed to the provision of one or more channels, each having an associated discharge opening, which are formed in the web of the valve plate to couple the reversing capacitance in fluid communication sequentially with each of the cylinder bores passing across the web.
According to one exemplary embodiment of the invention, at least two such channels are provided which are arranged on an arc defined by the low and high pressure connection ports. Optionally, the discharge openings and their associated channels may have the same or different diameters.
According to another exemplary embodiment of the invention, particularly if two channels are provided, the discharge openings of the channels are connected with each other via a recess formed in the web of the valve plate, such recess surrounding the discharge openings.
For a further improvement of a positioning of the cylinder bores the discharge openings of the channels extending from the reversing capacitance to each of the cylinder bores via the web formed on the valve plate are equipped with adjoining guide-in notches and/or guide-out notches. In one exemplary embodiment, the first discharge opening relative to the direction of rotation of the cylinder block is provided with a longer guide-in notch and a shorter guide-out notch adjoining the discharge opening. In addition, in the case of two channels being formed through the valve plate web, the second discharge opening relative to the direction of rotation of the cylinder block is provided with a shorter guide-in notch and a longer guide-out notch. Similarly, if a recess is formed surrounding the discharge openings of the two channels, this recess may be provided with a guide-in notch and/or a guide-out notch.
The present invention, accordingly, comprises the apparatus and method possessing the construction, combination of elements, and arrangement of parts and steps which are exemplified in the detailed disclosure to follow. Advantages of the invention includes an axial piston pump construction which reduces undesirable high-pressure-side pulsations. These and other advantages will be readily apparent to those skilled in the art based upon the disclosure contained herein.